Multi frequency microstrip filter detector

ABSTRACT

A filter-detector for selecting one or a number of narrow band microwave signals from either a wide band of microwave signals or from a source of spurious signals including a microstrip circuit with coupling strips for coupling frequencies predetermined by resonators located on the circuit board and diodes at the output of each coupler branchline for detecting the signal.

United States Patent [1 1 Stiglitz et al.

[ MULTl-FREQUENCY MICROSTRIP FILTER-DETECTOR [75] Inventors: Martin R. Stiglitz, Waltharn; James C. Sethares, Lexington, both of Mass.

[73] Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC.

[22] Filed: Nov. 23, 1971 [2]] Appl. No.: 201,348

[52] U.S. Cl 333/6, 333/73 S, 333/83 R, 333/84 M [51] Int. Cl H0lp 3/08, HOlp 5/12, H03h 7/02 [58] Field of Search 333/1, 6, 9, 73 R, 333/73 S, 70 R, 83 R, 84, 84 M [56] References Cited UNITED STATES PATENTS 3,611,197 10/1971 Moore et a1. 333/73 S X 1 June 26, 1973 3,121,847 2/1964 -Pakan 333/73 R X 3,657,561 4/1972 Riekers et 333/72 X 3,560,884 2/1971 Moore et a1. 333/6 3,237,132 2/1966 Okaya 333/73 R Primary Examiner-Rudolph V. Rolinec Assistant ExaminerMarvin Nussbaum Attorney-=Harry A. Herbert, Jr.

[ 5 7 ABSTRACT A filter-detector for selecting one or a number of narrow band microwave signals from either a wide band of microwave signals or from a source of spurious signals 4 Claims, 4 Drawing Figures Patented June 26, 1973 2 Sheets-Sheet 2 INVENTORS Mmvrnv R. ST/GLITZ James 35 E 222 BACKGROUND OF THE INVENTION This invention relates generally to the filtering and detection of microwave signals and more particularly to the filtering and detection of multi-frequency microwave signals.

It is becoming increasingly difficult to utilize microwave radiation due to the large number of signals currently being generated and the vast range over which the signals travel. The problem is particularly severe with systems that travel high in the earths atmosphere or in space. The directional antenna has helped to curb the problem, but has not provided a solution where a system utilizes a multi-frequency signal. 7

When a system is constructed with a plurality of subsystems, it is often necessary to instruct the system with a multi-frequency signal. Prior art'devices to filter microwave signals include multiple cavity filters utilizing waveguides or coaxial cable. Although these filters do perform adequately in stationary systems where space is not a limiting factor and the number of frequencies is somewhat controlled, such filters are by far too heavy and bulky for mobile applications.

There is a need then for a multi-frequency microstrip filter-detector, where as many as 1000 frequencies might be detected in a space not significantly larger than a common shoe box. Thus far, the prior art has been unable to show such a system.

SUMMARY OF THE INVENTION The invention utilizes an etched or plated microstrip circuit board mounted in a modular frame. The frame is so constructed that any number of them may be stacked, thereby increasing the filtering-detecting ca pability with relative ease.

The circuit board has a central feed line located along its longitudinal axis for receiving a signal from an antenna or other signal generating source and terminates in a critical impedence. The terminating impedence is functionof the dielectric constant of the circuit board, the thickness of the substrate and the width of the conductors on the board.

Adjacent to the feed line are a predetermined number of branch circuits which terminate at an output plug mounted on the frame. Between each branch circuit and the central feed line is a dielectric resonator. Coupling takes place between the ce'ntral feed line, resonator and branch circuit, thereby sending a particular frequency to the branch output. Resonators are se- DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of the invention capable of detecting ten frequencies.

FIG. 2 is a side elevation view partly in section of the invention.

FIG. 3 is an illustration depicting the coupling action in the invention.

FIG. 4 is a perspective view of a plurality of filterdetector modules in a stacked configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, the multi-frequency microstrip filter detector is shown generally at 10, mounted within the frame module 12. The frame may be constructed of aluminum or other suitable light weight material.

The circuit board 14 has placed thereon a central feed line 16 having an input connector 18 and a terminal connector 20. Positioned adjacent to the feed line are a plurality of branch circuits as shown; however, a larger or smaller number may be used depending upon the design requirements.

Between the feed line 16 and each branch circuit 22 is a disk-shaped dielectric resonator 24. The resonators are affixed to the circuit board by a suitable adhesive, and may be fabricated to any desired geometry utilizing appropriate low loss high dielectric materials such as SrTi0 Ti0 and CaTifl The resonators are preselected to perform a coupling action between the feed line and branch circuit. The particular material and configuration of the resonator will determine the frequency output of the branch circuit.

Distally of the centrally located feed line in each branch circuit is a Schottky-barrier beam diode 26. The diode receives the selected frequency signal and functioning as a detector provides an output to the plug 28.

The frame module is shown at 30 in FIG. 2. Output plugs 32 and input plug 34 and terminus plug 36 are mounted on the outside of the frame 30. The circuit board generally shown at 38 is formed of a dielectric substrate 40 having a ground plane 42 of 'a conductive material. Etched or otherwise placed on the opposed surface of the substrate is the microwave circuit 44.

FIG. 3 is an illustrative representation of the coupling which takes place between the feed line and branch circuit in the invention. The dielectric substrate 46 is mounted on the conducting ground plane 48. The feed line 50, containing the wideband signal, is critically spaced from the resonator 52 whereby flux lines 54 cause the preselected resonance and a signal 56 to be generated in the branch circuit 58. The size, shape and material of the resonator, as well as its position determine the frequency of the coupled signal onto the branch circuit.

In FIG. 4 there is shown a plurality of filter-detector circuits in a stacked configuration. The frame modules 60 are in juxtaposition with the centrally located circuit boards sufficiently spaced to prevent interaction between the electromagnetic fields. The end frame modules are covered with a plate 62 (shown in phantom) which is held in position by thebolts 64 which pass through holes 66 and align and secure the frame modules. The bolts are secured by nuts (not shown) or they may engage an electronic chassis as may be dictated by system design.

Having thus described our multi-frequency microstrips filter-detector we make the following claims as our invention:

l. A multi-frequency filter detector comprising: a frame; a dielectric circuit board mounted within the sition with said dielectric circuit board.

3. A multi-frequency filter detector according to claim 1 wherein said coupling means includes a dielectric resonator.

4. A multi-frequency filter detector according to claim 1 wherein, said detector means is a Schottleybarrier beam diode. 

1. A multi-frequency filter detector comprising: a frame; a dielectric circuit board mounted within the frame; an input circuit means mounted centrally of said frame and extending the length thereof; a plurality of output circuit means placed adjacent said input circuit, on either side thereof, in a spaced relationship, said output circuit means including means for coupling a selected frequency from said input circuit means and detector means to provide an output signal.
 2. A multi-frequency filter detector according to claim 1 a conductive ground plane mounted in juxtaposition with said dielectric circuit board.
 3. A multi-frequency filter detector according to claim 1 wherein said coupling means inclUdes a dielectric resonator.
 4. A multi-frequency filter detector according to claim 1 wherein, said detector means is a Schottley-barrier beam diode. 